Vapor generating and superheating operation



P- S. DICKEY 8 Sheets-Sheet 1 mVENmR.

PAUL s. DICKEY BY TfRNEY Dec. 7, 1965 VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29, 1951 at a a a3 3? 52332533. 15 no. 5 n.

I; no: 3332323 0.; 2... 0

Dec. 7, 1965 P. s. DICKEY 3,221,714

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29, 1951 8 he 2 75 22 86 AIR GAS 87 FLOW TEMP 1 ea -I -I g l I I 8| 83 I m 77/ I so AMPLIFIER I 82 4 76 78 j 89" 28 FINAL STEAM TEMP JNVENTOR.

PAUL S. DICKEY guww ATTORNEY Dec. 7, 1965 P. s. DICKEY 3,221,714

VAPOR GENERATING AND SUPERHEA'I'ING OPERATION Original Filed June 29, 1951 8 h et 3 00 0000 0 oo oqoo o 000 0 0o OJOOTCIOO 000 o 00 0100 0 J00 J o 00 0 '10 0 -00 o oo o o 0 do o oo o o o .10 o co 0 o o ,o

o oo o 0 Q Q TC-ZQO oo o o o oo 0 0 0 0 o 00 o o o o o oo o o o o 0 00 0 o D o 0 0 oo o o o o o 00 o o o o o oo o o Q o o oo o o o o 3 o oo o o o ,o

o oo o ,o 0 Jo SCREEN-3 0 oo 0 do 0 do 0 oo 0 on 0 U0 "fik o oo o oo o oo o on 0300 o 000 o 00 0000 o 00 0000 #o o oo oooo ooooo SECONDARY SUPERHEATER'4- REHEATER'S PRIMARY SUPERHEATER'6 FIG. 5

INVENTOR.

PAUL S. DICKEY ATTORNEY Dec. 7, 1965 P. s. DICKEY VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29, 1951 8 Sheets-Sheet 4 FINAL STEAM TEMP STEAM PRESSURE AIR HEATER 0 ECONOMIZER o -o o o o o o o o o o R YE RA AE w E P U S REHEATER SECONDARY SUPERHEATER GENERATING SECTION INVENTOR.

- PAUL S. DICKEY GAS FLOW PATH FIG. 6

8 Sheets-Sheet 5 INVENTOR.

P. S. DICKEY VAPOR GENERATING AND SUPERHEA'IING OPERATION- Original Filed June 29, 1951 Dec. 7, 1965 Dec. 7, 1965 P. S. DICKEY VAPOR GENERATING AND SUPERHEA'I'ING OPERATION 8 Sheets-Sheet 6 Original Filed June 29, 1951 AIR HEATER o o o o o o o 0 ECONOMIZER 7 OOOO PRIMARY SUPERHEATER SECONDARY SUPERHEATER GENERATING SECTION GAS FLOW PATH FIG. 8

FINAL STEAM TEMP INVENTOR.

PAUL S. DICKEY ATTORNEY Dec. 7, 1965 P. s. DICKEY 3,221,714

VAPOR GENERATING AND SUPERHEATING OPERATION Original Filed June 29, 1951 Y 8 t h 7 SI 22 28 ,f f f FINAL WATER GAS FLOW TEMP INVEN TOR.

PAUL S. DICKEY 9 'gmmw ATTORNEY United States Patent 3,221,714 VAPOR GENERATING AND SUPERHEATING OPERATION Paul S. Dickey, East Cleveland, Ohio, assignor to Bailey Meter Company, a corporation of Deiaware Application June 29, 1951, Ser. No. 234,169, now Patent No. 2,985,151, May 23, 1961, which is a division of application Ser. No. 57,686, Sept. 22, 1960,now Patent No. 3,136,300, dated June 9, 1964. Divided and this application Aug. 23, 1963, Ser. No. 304,034

. Claims. (Cl. 122-479) This is a division of my application Serial No. 57,686, filed in the United States Patent Ofiice on September 22, 1960, now Patent No. 3,136,300, being a division of my application Serial No. 234,169, filed June 29, 1951, now Patent 2,985,151.

My invention lies in the field of steam power generation and particularly in the control of steam temperature in connection with present-day vapor generators. Practically all central station capacity presently being installed, or on order, in the United States has rated steam conditions above 800 p.s.i.g. and 800 FTT; the highest operating temperature being 1050 FTT at pressures from 1500 p.s.i.g. to 2000 p.s.i.g. and rated load of from 500,000 to 1,000,000 110. per hr., with a large percentage employing reheat surfaces. The problems involved in the generation and close control of the properties of steam are quite dilferent now th-anwas the case at the time ofthe inventions in this field which are shown in the prior art.

Superheat temperature control is particularly desirable in the generation of steam for theproduction of electrical energy in large central station power plants. In suchplants the upper limit of superheat temperature is governed by the materials and construction of the turbine served by the steam. In the interest of turbine efficiency the temperature of the steam delivered to the turbine should be maintained within close optimum limits throughout a wide range of capacities.

As feed water temperatures progressively increase there is less and less work for the boiler proper, with the result that its convection heat-absorbing surface has disappeared to the point where the modern large utility unit consists ofa water-walled furnace, a convection superheater, an economizer and an air heater. Furnace design is now centering around sufficient water cooling surface to ab-; sorb the radiant heat and to achieve the required relatively low furnace exit gas temperatures.

With the superheating or resuperheating of the steam in one or more convection type heat exchange surfaces, the size and cost of such surfaces becomes a material factor in the total cost of the unit and any improvement leading to a reduction in the size of superheaters becomes of considerable importance. Usually these surfaces must be made of expensive high-alloy tubing to satisfactorily handle the temperatures and pressures encountered. V

It is thus a prime desideratum, in the design of such a unit, to proportion the steam generating surfaces and the steam superheating surfaces to give the desired final steam temperature at rated load. At peak load, in excess of the rated load, the final steam temperature will be in excess of that desired and correspondingly at lower ratings the steam temperature will not equal that desired. It is false economy to design the superheater for desired final steam temperature at peak load, for all loads below that value would then produce steam below the desired temperature. On the other hand, the design of the superheater to produce the desired final steam temperature at some rating below rated load would require an excessive cost of superheating surface and an lCe excessive final steam temperature throughout the upper ratings, with consequent danger to the turbine, or the necessity of extracting some of the surplus heat from the final superheated steam.

Thus, usually the heat exchange surface of the superheater is designed to provide the desired total temperature of the steam at rated load, and experience has shownthat below this load the total temperature of the leaving steam decreases while above this load the total temperature increases. This is because the characteristic curve of a convection superheater is a rising function with load as will be seen in FIG. 7 of the present application.

To reach the desired high superheated steam temperature, but not exceed it, requires exceedingly careful proportioning of the heat absorbing surfaces both for generating steam and for superheating it. But even if the desired superheated steam temperature be just attained initially by very careful designing at rated load, the superheated steam temperature will vary during operation by reasons of changes in cleanliness of the heat absorbing surfaces. Slag will form and adhere to the heat absorbing surfaces in the furnace thereby reducing the effectiveness of such surfaces and raising the furnace outlet temperature of the products of combustion. Furnace outlet temperature will also change with percentage of excess air supplied for combustion, with the characteristics of the fuel burned, and with the rate of coinbustion and the corresponding rate of steam generation. All of these things will therefore affect the temperature of the gases leaving the furnace and supplied to the superheater, whether the superheating elements are located in the furnace where they absorb heat by radiation from the burning fuel and products of combustion, or whether they are located beyond the furnace where they absorb heat by convection from the products of combustion only.

With the furnace volume, as well as the vapor generating furnace surface, and the vapor superheating surface, fixed and invariable, the possibility of satisfactorily controlling the final steam temperature lies in controlling the volume and temperature of the gases contacting the superheating surfaces. Total fuel and air supply are varied with demand or rating to provide desired steam flow output. Furnace temperature of the flame and products of combustion does not vary greatly with rating. This leaves the controllable variables, the volume and temperature of the gases entering the convection superheating surfaces. The volume, or mass flow rate, has been controlled in the past through by-passing some of the gas flow around the superheater surface. The temperature of the entering gases may be controlled by selecting the amount of generating surface to be contacted by the gases before they enter the superheater. It is also known to have spray attemperators or other heat absorbing means for the excess heat in the final steam before the steam goes to a turbine.

For any given furnace, as load increases, the heat input is increased, but the rate of heat absorption does not in crease as rapidly as the rate of heat input; therefore, the furnace leaving temperaturewill rise. With both the quantity rate and the temperature of the gases leaving the furnace increasing with load, it is apparent that a fixed surface convection superheater will receive a greater heat rate at higher loads than at lower loads and the heat transfer area is usually designed for the volume and temperature of leaving gases at rated load. Any further increase in heat release rate supplies to the fixed superheater surface more heat by gas volume and by gas temperature than it is designed for and a corresponding excessive final steam temperature is experienced. Correspondingly, at operation below the rated load the fixed superheater surface receives less volume and a lower temperature of gases leaving the furnace with corresponding low ering of final steam temperature leaving the superheater. It is therefore a principal object of my invention to provide an improved method and apparatus for extracting excessive heat from the steam at high rating and for supplying additional heat to the steam at low ratings, to the end that the final steam temperature will approximate a uniform value over a range of opearting ratings at each side of the rated load value.

It is known to control the primary heat absorption in a radiant furnace-by directionally controlling the firing as to the furnace surface in relation to the superheater surface. The known tangentially placed tilting burners allow a control of varying utilization of the furnace heat absorbing surface through the tilting of the burners. It is also known to use tilting burners in systems wherein the excessive heat in the upper ratings is absorbed by spray attemperation or is by-passed around the superheater by means of a by-pass damper; and to increase the heat rate which is directed at the superheater, relative to that which is directed to the generating surface, at the lower ratings. Such controls may be accomplished in sequence, or with, or without, overlap at the normal operating point.

I purposely employ selective distribution of load between vertically tiltable burners proportioning the application of heat as between steam generating surface and steam superheating surface at different loads. I vary the heat release direction and consequently the effective furnace absorption area. In other words, as rating falls I utilize proportionately less of the generating surface and thus tend to maintain the temperature of the gases entering the superheating surfaces more nearly constant than would otherwise be the case. This is accomplished by controllably tilting the vertically spaced, tangentially firing burners to the end of directionally applying the heat of combustion to the generating surface in accordance with rating.

My present invention has as a primary object method and apparatus for operating, and controlling the operation of, such vapor generating units through the utilization of more advantageous indexes of heat availability to the convection superheater and of operation of the unit as a whole.

So far as I am aware no one has previously used the actual entering gas temperature as an element in method and apparatus for controlling steam final temperature on units of the type under discussion equipped with tangentially firing tiltable burners. Attempts have been made to ascertain continuously the temperature within the superheater tubes near the entrance, near the exit and at intermediate locations. Attempts have also been made to obtain the temperature of the steam before it enters the convection superheater and to use this temperature measurement in conjunction with the final steam temperature, in controlling spray attemperators, gas by-passes, and the like. These methods and arrangements have not been entirely satisfactory. A considerable time and heat lag occurs in the heat transfer through the films and metal of the tube surfaces, and with rapidly fluctuating heat release loads and temperature effects as caused by slagging or deslagging of the furnace walls with corresponding fluctuating variations in heat absorption of the generating surface as well as flame drift around the furnace, has introduced lags in final steam temperature control systems with corresponding hunting and over-shooting. Through the use of my invention I avoid these inaccuracies and adverse effects by utilizing the actual furnace gas exit temperatures as an element in my control system to maintain final steam total temperature.

In the drawings:

FIGS. 1, 2 and 3 are somewhat diagrammatic sectional elevations of a vapor generating unit having primarily radiant generating surface and convection superheating surface.

FIG. 4 is a section taken along the line 4-4 of FIG. 1 in the direction of the arrows.

FIG. 5 is a section taken along the line 55 of FIG. 1 in the direction of the arrows and to a different scale.

FIG. 6 is a diagrammatic showing of my invention in connection with tilting burners and a gas by-pass damper.

FIG. 7 is a graph of characteristic values in connection with other figures of the drawing.

FIG. 8 is a diagrammatic showing of my invention in connection with tilting burners and a spray type attemperator.

FIG. 9 is another arrangement of tilting burner and spray attemperator control.

FIG. 10 is a diagrammatic showing of my control system in connection with steam superheaters and reheaters.

FIG. 11 diagrammatically illustrates a further embodiment of my invention.

FIGS. 1, 2 and 3 show in somewhat diagrammatic sectional elevation a typical vapor generator in connection with which I will explain my invention. FIG. 4 is a section, to somewhat different scale, along the line 44 of FIG. 1, in the direction of the arrows.

The generator is of the radiant type, having a furnace 1 which is fully water-cooled with the walls 2 of vertical closely spaced plain tubes constituting the vapor generating portion of the unit. Products of combustion pass upwardly through the furnace 1 in the direction of the arrow, through the tube screen 3, over secondary superheater surface 4, a reheating section 5 and a primary superheating surface 6. A tubular economizer section 7 follows the superheater 6 and in turn may be followed by an air heater.

While my invention is applicable to generating units empolying fuel burned in suspension, such as gas, oil, or pulverized coal, the most prevalent use at present of tilting burners is with pulverized coal.

The unit is fired with pulverized coal from four sets of corner located tangential burners, vertically-adjustable or tiltable through a range of approximately +30 to horizontal to -30. FIG. 4 diagrammatically shows the firing arrangement of the four corner burners at a given elevation or section. I have shown in FIGS. 1, 2 and 3 that each corner set has four vertically spaced burners, a total of 16 for the unit. I designate (FIG. 4) the four vertical sets by the reference characters 10, 11, 12, 13 and in general indicate that the four burners of a vertically spaced set are tiltable together, although it is possible that other combinations of the 16 burners may be had for relative movement.

FIGS. 1, 2 and 3 are substantial duplicates except for illustrating the effect upon furnace flame location of burner tilting. In FIG. 1 the burners are horizontally firing or at what I designate a zero tilt position. The general flame location is diagrammatically illustrated.

In FIG. 2 the burners are shown depressed or in a downward tilt of some 25 and it is evident that more of the generating wall surface 2 is contacted than was the case in FIG. 1.

In FIG. 3 the burners are illustrated as having an upward tilt of approximately 25 and it is here evident that a considerable lower portion of the wall generating surface 2 is not directly contacted by the radiant heat of the flame body.

These illustrations show how the flame body can be raised or lowered over a considerable distance to make use of more or less furnace heat absorption surface and thereby proportion the amount of heat subjected upon the generating surface compared to that subjected upon the superheating surface and thus effecting wide range control over the gas temperatures leaving the furnace at the screen tubes 3. By thu providing control of furnace heat absorption the effect is similar to that which would be accomplished by the ability to increase or decrease the size of the furnace surface at will relative to a fixed convection superheating surface.

An upward tilting of the burners tends to increase steam temperature while a downward tilting tends to reduce steam temperature for any given load. The effect of the tilt is to cause the zone of active combustion in the furnace to raise or lower, decreasing or increasing the effective radiant heat absorbing surface in the furnace and to consequently increase or decrease the temperature of the gas entering the superheater.

I have found that a most desirable index of heat available to superheat the steam is a continuous measure of the temperature of the gases immediately prior to their contacting the superheating surface. In a unit of the size and type being described the temperature of the gases first contacting the convection superheating surface should be in the neighborhood of 2000 F. for a steam final temperature of 1000 FTT and under different conditions of operation will be in the range of 1700-2300 F. When there is a change in furnace exit gas temperature, for any reason, there is of necessity a time lag of heat transfer and metal temperature stabilization before the gas temperature change is reflected in final steam temperature change. Thus the use of actual gas temperatures prior to convection heat exchange as an operating guide or control index anticipates the effect of the gas temperature change upon the superheating of the steam.

I have found it possible to provide a continuous determination of furnace exit gas temperatures by means of a bolometer or other radiation sensitive device as well as bare metal thermocouples or high-velocity thermocou les,

In FIG. 1 I designate certain temperature determining locations to which reference will later be made. Representative of furnace exit gas temperature is location A at the entrance to tube screen 3; location B is the gas entrance to secondary superheater 4; C represents gas en trance to reheat surface 5; D is the location at entrance to primary superheater 6; and E is between the primary superheater and the economizer 7. I expect that the gas temperature at locations A or B will be in the range 1700- 2300 F. while at locations C, D or E the gas temperatures will be in successively lower ranges as the heat of the gases is transferred to the steam.

I preferably employ a radiation sensitive device at 10- cations A and B and will refer to a bolometer as satisfactorily representative. The bolometer of the Rutherford et al. Patent 2,524,478 has been successfully used as a device sensitive to total thermal radiation for producing an effect representative of the energy level of radiation re ceived. The patent to English et al. No. 2,624,012 dated December 30, 1952 discloses and claims a circuit including the bolometer for actuating a recorder-controller in terms of temperature.

In FIG. 5 I show somewhat diagrammatically a section taken through the unit of FIG. 1, along the line 5-5, in the direction of the arrows. The locations A, B, C and D are not necessarily spot locations but are areas or planes between the various heat transfer surfaces. At I designate a bolometer or other radiation receptive head sighted across A and at 16 a similar head sighted across B. These devices may preferably operate in the range 1700-2300 F. I have also found that bare metal thermocouples or high velocity thermocouples may be used to obtain gas temperatures in locations A and B if proper precautions are taken against the corrosive, and erosive efiects of the gases and entrained solid matter.

By way of example I illustrate in FIG. 5 four bare metal thermocouples TC1, TC-2, TC-3 and TC-4 spaced across the area A in front of the screen tubes 3. These are preferably spaced across the screen tubes 3 and are connected in series with each other in a measuring bridge network to obtain an average of the temperatures to which they are subjected. Preferably the thermocouples are suspended downwardly through the roof of the unit until the thermocouple ends are in a line across the entrance to the screen 3 at about location A of FIG.

1. The thermocouple itself is encased in a thin wall protecting tube to protect it against the erosive and corrosive action of the gases but may under certain conditions be bare. When encased in a thin tube protector the latter is fastened to, and suspended from, an alloy tube which encases the lead wires upwardly to, and through, the roof. Such a construction has been found to have a reasonably long life and to satisfactorily obtain an accurate average of the temperatures across the location A.

A similar use of thermocouples may be had through the area B or the area C. In FIG. 5 I show an alternate possible construction where the thermocouples TC-10, TC-20, TC-30 and TC-40 are projected through, and horizontally from, the rear of the unit assembly on supporting pipes which additionally act as protectors of the lead wires.

Regardless of the type of temperature sensitive device, or its mode of installation, the result is to obtain the actual temperature of the gases rather than any metal temperature or steam temperature in the various locations.

Referring now to FIG. 6 I show therein in very diagrammatic form the gas flow path in relation to the different heat exchange surfaces. Around at least a portion of the superheating surfaces 4, 5 and 6 I diagrammatically show a gas by-pass duct 17 having therein a control damper 18 positionable by a control drive 19. Positioning of the damper 18 allows a controllable portion of the heated gases leaving the furnace to by-pass some of the superheating surface to the entrance of the economizer section 7 and thus to be ineffective in superheating the generated steam.

At 20 I show a control drive arranged to tilt the set of four vertically spaced burners 10, preferably through an angle +30 from the horizontal. In this figure I have shown only a single vertically spaced set of burners 10 as representative of the four corner sets previously mentioned and shown in FIG. 4. It will be appreciated that the showing of FIG. 6 is diagrammatic and the control drive 20 may be considered as simultaneously adjustably tilting all four sets of burners 10, 11, 12 and 13.

In the present arrangement the bolometer 16 is sensitive to gas temperatures at location B and is arranged to activate a recorder-controller 22 continuously positioning the stem 23 of a pneumatic pilot valve 24 to establish in a pipe 25 an air loading pressure representative of the average temperature of the gases at location B. The pilot valve 23, 24 is of a known type as disclosed in the Johnson Patent 2,054,464 and is so arranged in the present disclosure that an increase in temperature at location B results in an increase in the air loading pressure within pipe 25.

The temperature of the gases entering the steam superheating surfaces is an index of the heat available for superheating the steam. Many factors may contribute to variation of temperature of the gases entering the convection heating surfaces. Change in demand, with consequent increase or decrease in fuel-air admission rate will change the gas mass flow as well as its velocity and temperature. As an index of demand I show a Bourdon tube 21, sensitive to steam pressure, and arranged to position a pilot valve 21A to control total fuel and air supply rate. The demand index may be rating, such as steam flow rate or air flow rate, and may include a basic tilting of the burners in accordance with demand load upon the unit. For steady state demand, the furnace exit gas temperature may vary from such causes as flame waver resulting in varying generating surface absorption, slagging or deslagging of generating surface,

burnability of the fuel, etc. Regardless of the cause of the variation, the fact remains that a variation in such temperature may cause an undesired deviation in final steam temperature from the desired value.

The temperature of the gases at the entrance to the superheating surface is therefore a cause index materially in time advance of any effect index such as metal or steam temperature of the superconducting surfaces. By utilizing such cause index I may anticipate its effect upon the final steam temperature and provide an initial coarse adjustment to be verniered by final steam temperature toward the desideratum.

Referring again to FIG. 6 I show therein at 28 a recorder-controller of final steam temperature arranged to position the movable element 29 of a pilot valve 30 continuously establishing in a pipe 31 a fluid loading pressure representative of final steam temperature. In the example being described, it is desired to maintain a final steam temperature of 1000 FTT as nearly constant as possible regardless of demand. It will be understood that the generating and superheating heat exchange surfaces are so designed and proportioned as to give a final steam temperature of 1000 FTT at rated load operation. The characteristics of such a radiant furnace generator with convection heated superheating surfaces predicates a tendency toward excessive final steam temperature for peak load and a deficiency in final steam temperature for loads below the design rated value.

In FIG. 7 I show the characteristic curve of such a convection superheater designed for final steam temperature of 1000 FTT under rated load operation. From FIG. 7 it will be seen that desired control operation is to remove the possibility of excessive steam temperature at peration or by-passing the gas around the superheating the higher ratings and to raise the deficient steam temperature at lower ratings. In general I accomplish this either by removing excessive heat through spray attemsurface at the higher ratings while, at the lower ratings, I raise the characteristic temperature through proportioning the generating and superheating surfaces by tilting the fuel burners.

FIG. 6 shows such a control system utilizing a control of burner tilting and gas by-pass damper operation which may be simultaneous or in desired sequence. Usually the initial response of the control system is applied to the burner tilt control drive 20. When the burners are tilted downward to out of their travel (adjustable), action is transferred through sequence operation of a relay to the by-pass damper.

It will be seen that the air pressure loading line 31 joins the A chamber of a standardizing relay 32 which may be of the type described and claimed in Gorrie Patent Re. 21,804 and whose output communicates with a pipe 33. Such a relay provides a proportional control with reset characteristics. It provides for the final control index (final steam temperature) a floating control of high sensitivity superimposed upon a positioning control of relatively low sensitivity. A function of the adjustable bleed connection in the relay 32 is to supplement the primary control of the pressure effective in pipe 31 with a secondary control of the same or of different magnitude as a follow-up or supplemental action to prevent overtravel and hunting.

The output of the relay 32, available through the pipe 33, is admitted through an adjustable bleed valve to the C chamber of an averaging relay 34, to the A chamber of which is connected the pipe 25. The relay 34 may be of the type described and claimed in my Patent 2,098,913.

The output of relay 34 is available in a pipe 35 branched as at 36, 37 to the control drives 19 and 20 respectively. Positioned in the pipes 36 and 37 are manual-automatic selector valves 38, 39 respectively which are preferably of the type disclosed in the patent to Fitch 2,202,485 providing a possibility of hand or automatic control of the damper 18 or the tilting burners respectively.

The necessary, and known, adjustments are provided in the recorders-controllers 22, 28 as well as in the relays 32, 34 and in the control drives 19, 20, to the end that the tilting burners and by-pass damper may be biased the one relative to the other or may be sequentially responsive to the control indexes. For example, the loading pressure values available in the averaging relay 34, from pipes 33 and 25, may be so adjusted that the tilting burners will be operated through certain ranges and then sequentially the by-pass damper will be moved. The sequence may be a successive one or with adjustable overlap as will be explained in connection with FIG. 7.

The operation of FIG. 6 is as follows. It will be understood that the response rate of bolometer 16 and its recorder-controller 22 may be adjusted to rapidly fluctuating gas temperatures to produce an averaging effect, if desired. Assuming a steady state of operation, an increase in temperature at location B indicates an increase of heat available for superheating the steam and under steady state operation it may be assumed that such an increase would cause an undesirable increase in steam final temperature. Thus I provide that an increase in temperature at location B will increase the loading pressure value Within pipe 25 and within the A chamber of relay 34. This produces an increase in pressure within the D chamber of relay 34 and thus in the pipes 35, 36 and 37. Preferably, an increase in pressure in pipe 37 actuates the control drive 20 to tilt the burners 10 downwardly thus increasing the heat absorption of the generating surface and abstracting some of the available heat from the furnace gases prior to their reaching location B.

The components of the system may be so adjusted that, after the burners have been tilted downwardly to the predetermined maximum amount, the travel of control drive 20 will cease and the control drive 19 will become effective to begin to open the by-pass damper 18 and by-pass some of the available heating gases around at least a portion of the superheating surface.

Assuming for the moment that the temperature of the entering gases at location B is unvarying, then an increase in final steam temperature results in an increase in air loading pressure in pipe 31 and in the A chamber of relay 32, and correspondingly in pipe 33 which joins the C chamber of relay 34 through an adjustable restriction. An increase in air loading pressure in the C chamber of relay 34 acts in the same direction as an increase in air pressure within chamber A and, as previously explained, results in a downward tilting of the burners 10 and later an opening of the by-pass damper 18.

Conversely, a decrease in gas temperature at location B, or a decrease in final steam temperature, results in a closing off of the gas by-pass damper 18, and an upward tilting of the burners 10 to decrease the generating surface heat absorption and raise the temperature of the gases entering the superheating surface.

Referring now to FIG. 7 it will be seen that the burner tilt and by-pass damper operations may be sequential, with or without overlap. The system may be so adjusted that through a predetermined span across the rated load point there is an overlapping operation of both the damper 18 and the burners 10 to the end that one may be attempting slightly to raise steam temperature while the other is counteracting this in attempting to lower the steam temperature. In certain installations this overlap may be desirable to prevent hunting from one control to the other if the sequence is as may be termed end-to-end or with a gap between the stopping of one control drive and the starting of the other. In any event the necessary adjustments are provided in the various components of the system to provide a smooth transition across the rated load point of FIG. 7. Normally the control is on the tilting of the burners and it is only when We get to the limit of range that the by-pass damper or attemperator is used.

By way of example only, I illustrate at the upper portion of FIG. 7 a characteristic burner tilt curve where X indicates the crossing of the characteristic curve with the zero tilt position of horizontally operated burners. The pick-up or beginning of movement of the tiltable burners may be shifted to the right or the left (in FIG.

7) so that the characteristic curve may be moved to the right or to the left relative to point X and with such movement the efiectiveness of the burner tilt upon the final steam temperature.

Referring now to FIG. 8 I show therein an arrangement somewhat similar to that of FIG. 6 except utilizing a spray attemperator between the primary superheater 6 and the secondary superheater 4 to remove excess heat from the steam, as an alternate to the ga bypass of FIG. 6. The general operation of the system is the same and the function (FIG. 7) of the attemperator in the one case and of the by-pass damper in the other case is to prevent final steam temperature from rising above the desired value at peak loads. With the by-pass damper control of FIG. 6 some of the heating gases, heated at an excessive temperature, are by-passed around the superheating surface. With the arrangement of FIG. 8 all of the gases are allowed to pass through the superheating surface but some of the excessive heat in the steam is extracted by spray attemperation between the superheaters. The arrangement of FIG. 8- may, or may not, have a reheat section such as was shown at in FIG. 6, but it is immaterial insofar as operation of FIG. 8 is concerned.

The arrangement of FIG. 8 is substantially identical with that of FIG. 6 except that in the former t.e pipe 36 leads to a diaphragm actuated control valve 40 for controlling the flow of attemperating water through a pipe 41 to an attemperator 42 serially located between the primary superheater 6 and the secondary superheater 4 in the fluid flow path. The attemperator 42 is preferably of the type described in the patent to Fletcher et al. No. 2,550,683 wherein the superheated steam conduit has therein a Venturi acting as a part of a thermal sleeve to protect the conduit against thermal stresses. Forwardly of the entrance of the Venturi is a spray nozzle through which water is atomized in a conical spray which is enveloped by the high velocity superheated steam. The nozzle is thus disposed in a relatively low velocity zone so there is a low pressure loss due to turbulence created by the nozzle body. The water leaves the nozzle in the form of a spray cone with a hollow vortex, the outer limits of this cone being within the entrance surfaces of the Venturi.

In FIG. 9 I show an arrangement in some respects similar to that of FIG. 8 but incorporating refinements thereover. The control of the four corner sets of tiltable burners 1t), 11, 12 and 13, by way of their separate control drives 20, 20A, 20B and 20C, is conjointly under the dictates of the gas temperature controller 22 and the final steam temperature controller 28, as in FIG. 8. The pipe 37, beyond the manual-automatic selector valve 39, is branched as at 45, 46, 47 and 48 to the four control drives. I may locate in each of the branches a manual-automatic selector valve 49 and through the agency of these four selector valves I may bias one or more of the vertical sets of burners relative to the other sets or may adjust any of the sets individually by remote manual means.

In this embodiment I introduce a measure of the flow rate of the water passing through the conduit 41 to the attemperator 42. Positioned in the pipe 41 is an orifice 50 for producing a pressure differential representative of the fluid flow rate and to which pressure differential a water flow rate meter 51 i continually responsive. The meter 51 positions the movable element 52 of a pilot valve 53 continuously providing in a pipe 54 a fluid loading pressure representative of the flow rate of water to the attemperator 42.

I provide at 55 a differential standardizing relay to the A chamber of which is connected the pipe 35 carrying the output of averaging relay 34. To the B chamber of relay 5'5 I connect the pipe 54 thus providing that the relay 55 is subjected to the difi'erential action of the loading pressures within pipes 35 and 54 respectively.

The output of relay is available through a pipe 56 to the positioner 57 of a control valve 40. Each of the control drives 20, 20A, 26B and 20C are provided with positioners 58 and the positioners 57, 58 may be of the type disclosed and claimed in the Gorrie et a1. Patent 2,679,829 dated June 1, 1954. Such positioners of the valve 44) and of the burner tilting control drives insure that the valve and the burners are positioned to the actual positions wanted, for the positioners incorporate a characterization of the characteristic response curve of each of the controlled elements thus correcting for any non-linearity of such response curves as well as for differences in response friction, capacities, and the like between the different control elements. Adjustments are provided whereby the control elements may be biased one relative to the other if desired.

In the system of FIG. 9 I introduce the water flow rate index to take care of feed pump variations, etc., which may otherwise affect the amount of water supplied to the attemperator 42 for any given control pressure subjected upon the pipe 56. In other words, the water flow rate index provides a tie-back to insure that the correct amount of water is used for spray attemperation to accomplish the purpose desired.

The relay 55 receives in its A chamber a loading pressure representative of desired water valve positioning called for by the indexes, gas temperature and final steam temperature. To this leading pressure is opposed the loading pressure representative of water flow rate, subjected upon the B chamber of the relay 55, to the end that if the water flow rate is as desired, the two loading pressures will tend to neutralize each other and no change in the loading pressure within the pipe 56 will be made. If, however, the pressure in chamber A or that in chamber B deviates, then the differential between the pressure effects in the chambers A and B will be effective to vary the loading pressure within the pipe 56, effective in positioning the valve 46, until the increased or decreased rate of how of water through the pipe 41, acting through the flow meter 51 and pipe 54 again brings the relay 55 to a balance condition.

Refer now to FIG. 10. In FIGS. 1, 2, 3, 5 and 6 I have indicated a reheat superheating surface 5 located (in the gas path) between the secondary super-heater 4 and the primary superheater 6. In FIG. 10 I illustrate my invention as applied to the control of the final temperature. of the reheated steam as well as to the final temperature of the original steam. The drawing shows at the left-hand side the flow path of steam from the generating section through the primary superheater 6, the spray type attemperator 42, and the secondary superheater 4 to the turbine. On the right-hand side of the drawing I illustrate that steam returned from the turbine passes through a controllable spray type attemperator 60 before entering the reheater section 5. Water to the attemperator 64 is furnished through a pipe 61 under the control of the regulating valve 62. It will be understood that the vapor passing through the reheater 5 does not necessarily have to be the same vapor that passed through superheaters 4 and 6, but may come from any source.

In general, the spray type attemperator 42 is under the conjoint control of the gas temperature controller 22 and the final steam temperature controller 28 in manner similar to that described in connection with FIG. 8. The spray type attemperator 60 is under the control of the gas temperature controller 22 and the reheated steam temperature controller 63.

The controller 63 is arranged to position the movable element 64 of a pilot valve 65 continually establishing in a pipe 66 a fluid loading pressure representative of final reheated steam temperature leaving the reheater section 5. Pipe 66 joins the A chamber of a standardizing relay 67 whose output pipe 68 joins the C chamber of an averaging relay 69. The pipe 25 from the gas temperature controller 22 joins the A chamber of the relay 69. Thus the relay 69 provides in its output pipe 70 a resultant fluid loading pressure, the result of the pressures in pipes 25 and 68. The pipe 70 joins pipe 72 through manualautomatic selector valve 73 to the control valve 62.

I have shown in FIG. that the control drive (representative of power means for tilting all sets of burners) receives its air loading pressure from a pipe 71, through selector device 39, from a selective relay 95. With this arrangement the burner tilting is selectively under the control of either final steam temperature or reheated steam temperature.

The tilting of the burners is primarily to raise steam temperatures at lower ratings and it is possible that either the final steam temperature or the reheated steam temperature is sufficiently high that, were it the sole dictator of burner positioning, the signal would call for a depression of burner tilt. Such action would tend to reduce both final temperatures, thus further lowering the one that was already too low. It would be better to raise both, thus bringing the low temperature up toward desired value; the additional excess temperature of the already high one being taken care of by attemperation or by-pass. damper control.

The loading pressure of pipe is subjected upon the A chamber of selective relay 95, while the loading pressure of pipe '70 is subjected upon the B chamber in opposition. Thus the two loading pressures act against opposite sides of diaphragm 96. The spring of relay 95 is so adjusted that the relay force system is in balance when the two loading pressures are in balance and neither of the valves 97, 98 are open. The pipe 35 joins the inlet of valve 98 while the pipe 70 joins the inlet of valve 97. The arrangement is such that Whichever loading pressure is the lower, that is the one which is effective in establishing the pressure in pipe 71 to actuate control drive 20.

Assume that final reheated steam temperature (63) is lower than final steam temperature (28). The pressure in pipe 70 is less than that in pipe 35. Diaphragm 96 moves downwardly, opening valve 97 and admitting pressure from pipe 70 to the D chamber of relay 95 and to the pipe 71. The pressure in 70 is the lower one so that pipe 71 is always receptive of the lower pressure of pipes 35 or 70.

The various devices of FIG. 10 may be so adjusted that valves and 62 as well as drive 20 are sequentially effective in operation along the characteristic curve of FIG. 7.

Referring now to FIG. 11 I show therein a slightly different arrangement wherein I provide a control index representative of the total available heat at the entrance to the superheating surfaces, namely, an index representative of gas volume multipiied by its average temperature as indicative of its B.t.u. content.

An air flow meter 75 is responsive to the pressure differential existing across two points of the generating unit or may be connected across an air heater or other fixed restriction in the path of the excess air and products of combustion flowing through the unit. It is only important that the meter 75 provide a continuous rate measure of the total excess air and products of combustion passing the location B at the entrance to the superheating surfaces. By air flow I intend to include the rate of fiow of gaseous products of combustion and excess air passing through the unit and particularly the gaseous stream entering the superheating surfaces. As I have previously pointed out, the heat available to the superheating surfaces is the product of the gas mass flow and its average temperature.

The electronic calculating circuit of FIG. 11 is disclosed and claimed in the patent for Anthony J. Hornfeck No. 2,636,151 providing a result which is the product of air flow rate times gas temperature in terms of total heat available on a rate basis.

The flow meter 75 is arranged to continually position the movable core 76 of a transformer relative to an alternating current energized primary 77 and inductive secondaries 78, 79 and 8t). Across the bucking secondaries 79, 80 is an adjustable resistance 81 whose movable contact 82 is positioned by the gas temperature controller 22. The elements 79, 80, 81 and 82 are connected in a balanceable network including a resistance 83 and an adjustable contact 84 whose function is to balance the network. Upon displacement of the core 76 and/or the contactor 82 from a given position, the network becomes unbalanced and the extent of the unbalance is effective upon an amplifier 85 arranged to activate a motor 86 in one direction or the other for positioning the contactor 84 in proper direction and extent to rebalance the network. The particular characteristics of this network are such that the position of the contact 84 and the movable element 87 of a pilot valve 88 are representative of the product of air flow times gas temperature and may be calibrated in terms of B.t.u. rate. The pilot 87, 88 continuously establishes in a pipe 89 an air loading pressure representative of heat availability at the entrance to the superheating surfaces and the pipe 89 is joined to the A chamber of an averaging relay 34, to the C chamber of which is connected the pipe 33 carrying a loading pressure esta. lished by the final steam temperature controller 28. The output of relay 34- is effective through a pipe 35, selector valve 39, and pipe 37 to position the control drive 26 and the tiltable burners 10.

The operation of FIG. 11 is in general one of positioning the tiltable burners responsive to a continuous indication of heat availability at the entrance to the superheating surfaces with a check-back from actual final steam temperature.

The control system which I have illustrated and described finds, at the moment, its widest applicability in the burning of pulverized fuel but is equally effective in connection with vapor generating and superheating units adapted to be fired by any fuel burned in suspension including gas or vaporized oil.

While I have described in detail arrangements incorporating a continuous determination of gas temperature at location B through the agency of a bolometer, it will be appreciated that I contemplate the use at location B of any temperature sensitive device or devices which will provide a continuous determination of the temperature of the gases available at the entrance to the superheating surfaces as clearly distinguished from any metal temperature or temperature of the steam or other fluid within the heat transfer surfaces. Furthermore, I contemplate that under certain conditions of operation it may be highly desirable to utilize in my method and control apparatus a determination of temperature of the gas flowing stream at other locations, for example, at A, C, D or E.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a vapor generating and superheating unit of the type having a fluid-cooled combustion furnace with a heating gas outlet in one end portion thereof and having convection vapor superheating surface positioned beyond the combustion furnace outlet in the path of heating gas flow, the method of operation which comprises introducing fuel and air for combustion into the combustion furnace from a fixed location spaced from the gas outlet, varying the total fuel and air input rate in accordance with demand upon the unit for generated vapor of desired total heat content, and directionally varying the resulting combustion process in the furnace away from the gas outlet responsive to an increase of volume flow rate or of temperature of the heating gases entering the superheating surfaces, and toward the gas outlet responsive to a decrease of volume flow rate or of temperature of the heating gases entering the superheating surfaces.

2. In a vapor generating and superheating unit of the type having a fluid-cooled combustion furnace with a heating gas outlet in one end portion thereof and having convection vapor superheating surface positioned beyond the combustion furnace outlet in the path of heating gas flow, the method of operation which comprises introducing fuel and air for combustion into the combustion furnace from a fixed location spaced from the gas outlet, varying the total fuel and air input rate in accordance with demand upon the unit'for generated vapor of desired total heat content, anddirectionally varying the resulting combustion process in the furnace toward or away from the gas outlet conjointly responsive to a determination of heat rate availability in the heating gases entering the superheating surface and a determination of the final vapor temperature.

3. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion furnace with a heating gas outlet in the upper end portion thereof, fired with one or more fluent streams of fuel and air through fixed location in the combustion furnace wall spaced vertically downwardly from the heating gas outlet, and having convection superheating surface positioned beyond the combustion furnace outlet in the path of heating gas flow; the method of operation which comprises varying the total fuel and air input rate in accordance with demand upon the unit, and directionally varying the fluent stream upwardly or downwardly into the combustion furnace from the fixed vertical location as well as maintaining a substantially uniform optimum final steam temperature through controllably by-passing heating gases around at least a portion of the superheating surface both conjointly responsive to a determination of temperature of the heating gases entering the superheating surfaces and a determination of the final vapor temperature.

4. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion furnace with a heating gas outlet in the upper end portion thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion furnace, tiltable burner means for the fluent supply spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal directionally upwardly or downwardly of the combustion furnace relative to the heating gas outlet, means continuously determining the volume flow rate of gases entering the superheating surfaces, means continuously determining the temperature of the gases entering the superheating surface, and control means for the motive means responsive to both said determining means whereby the burner means is tilted downwardly as the volume flow rate of gases entering the superheating surfaces or the temperature of the gases entering the superheating surfaces increases and vice versa.

5. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion furnace with a heating gas outlet in the upper end portion thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion furnace, tiltable burner means for the fluent supply spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal directionally upwardly or downwardly of the combustion furnace relative to the heating gas outlet, means continuously determining the heat rate available of the gases entering the superheating surfaces, means continuously determining the final vapor temperature, and control means for the motive means sensitive to both said determining means.

6. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion furnace with a heating gas outlet in the upper end portion thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion furnace, tiltable burner means for the fluent supply spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal directionally upwardly or downwardly of the combustion furnace relative to the heating gas outlet, a by-pass passage for the heating gases around at least a portion of the superheating surfaces, damper means for the passage, means determining the temperature of the gases leaving the combustion furnace outlet, and means determining final vapor temperature, said motive means and damper means both under the control of said last two determining means.

7. In a vapor generating and superheating unit of the type having a fluid-cooled combustion chamber with a heating gas outlet in one end portion thereof and having convection vapor superheating surface positioned beyond the combustion chamber outlet in the path of heating gas flow, the method of operation which comprises introducing fuel and air for combustion into the combustion chamber from a fixed location spaced from the gas outlet, directionally varying the resulting combustion process in the chamber toward or away from the gas outlet in accordance with a determination of temperature of the heating gases entering the superheating surfaces, varying the total fuel and air input rate in accordance with demand upon the unit for generated vapor of desired total heat content, maintaining a substantially uniform optimum final total vapor temperature through controllably by-passing heating gases around at least a portion of the superheating surface, and controlling the bypassing responsive to a determination of temperature of the heating gases leaving the combustion chamber.

8. In a vapor generating and superheating unit of the type having a fluid-cooled combustion chamber with a heating gas outlet in one end portion thereof and having convection vapor superheating surface positioned beyond the combustion chamber outlet in the path of heating gas flow, the method of operation which comprises introducing fuel and air for combustion into the combustion chamber from a fixed location spaced from the gas outlet, directionally varying the resulting combustion process in the chamber toward or away from the gas outlet in accordance with a determination of temperatures of the heating gases entering the superheating surfaces, varying the total fuel and air input rate in accordance with demand upon the unit for generated vapor of desired total heat content, maintaining a substantially uniform optimum final total vapor temperature through controllably by-passing heating gases around at least a portion of the superheating surface, and controlling the by-passing conjointly responsive to a determination of temperature of the heating gases entering the superheating surfaces and a determination of the final vapor temperature.

9. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end portion thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion chamber, tiltable burner means for the fluent supply located through the combustion chamber wall spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal upwardly or downwardly of the combustion chamber relative to the heating gas outlet, means continuously determining heating gas temperature leaving the combustion chamber, control means for the motive means sensitive to said determining means, a by-pass duct for the heating gases around at least a portion of the superheating surface, and damper means for the duct, said damper means also responsive to said determining means.

10. In a vapor generating and superheating unit of the type having a vertically elongated fluid-cooled combustion chamber with a heating gas outlet in the upper end thereof, the combination of means supplying fuel and air for combustion in fluent form to the combustion chamber,

tiltable burner means for the fluent supply located through the combustion chamber wall spaced downwardly from the heating gas outlet, control means for the total fluent supply rate in accordance with demand upon the unit, motive means adapted to tilt the burner means from horizontal directionally upwardly or downwardly of the combustion chamber relative to the heating gas outlet, means continuously determining heating gas temperature leaving the combustion chamber, control means for the motive means sensitive to said determining means, a bypass passage for the heating gases around at least a portion of the superheating surface, damper means for the passage, measuring means of the final vapor temperature, said damper means positioned conjointly responsive to the heating gas temperature determining means and said measuring means.

References Cited by the Examiner FREDERICK L, MATTESON, IR., Primary Examiner.

KENNETH W. SPRAGUE, PERCY L. PATRICK,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,221,714 December 7, 1965 Paul S. Dickey It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, line 6, beginning with "Application June 29, 1951" strike out all to and including Ser. No. 304,034" in line 10, and insert instead Application Sept. 22, 1960, Ser. No. 57,686, now Patent No. 3,136,300, June 9, 1964, which is a division of application Ser. No. 234,169, June 29, 1951, now Patent No. 2,985,151, May 23, 1961 column 3, line 8, for "opearting" read operating column 7, line 28, strike out "peration or by-passing the gas around the superheating" and insert the same after "attem-" in line 31 same column 7 column 14 line 43 for "temperatures' read temperature Signed and sealed this 18th day of October 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A VAPOR GENERATING AND SUPERHEATING UNIT OF THE TYPE HAVING A FLUID-COOLED COMBUSTION FURNACE WITH A HEATING GAS OUTLET IN ONE END PORTION THEREOF AND HAVING CONVECTION VAPOR SUPERHEATING SURFACCE POSITIONED BEYOND THE COMBUSTION FURNACE OUTLET IN THE PATH OF HEATING GAS FLOW, THE METHOD OF OPERATION WHICH COMPRISES INTRODUCING FUEL AND AIR FOR COMBUSTION INTO THE COMBUSTION FURNACE FROM A FIXED LOCATION SPACED FROM THE GAS OUTLET, VARYING THE TOTAL FUEL AND AIR INPUT RATE IN ACCORDANCE WITH DEMAND UPON THE UNIT FOR GENERATED VAPOR OF DESIRED TOTAL HEAT CONTENT, AND DIRECTIONALLY VARYING THE RESULTING COMBUSTION PROCESS IN THE FURNACE AWAY FROM THE GAS OUTLET RESPONSIVE TO AN INCREASE OF VOLUME FLOW RATE OR OF TEMPERATURE OF THE HEATING GASES ENTERING THE SUPERHEATING SURFACES, AND TOWARD THE GAS OUTLET RESPONSIVE TO 